Ernst von Simson was born in Berlin on 7 April 1876 as the son of August (1837-1927) and Beate von Simson, née Jonas (1841-1913).
His grandfather was Eduard Simson, who was President of the Frankfurt National Assembly 1848/49 and 1st President of the Imperial Court of Justice 1879-1891.
Ernst von Simson came from a family that converted from Judaism to Protestant Christianity in the first half of the 19th century.
After finishing school in Berlin, he studied law in Leipzig, Lausanne and Berlin from 1894 to 1897. He then entered the Prussian judicial service, obtained his doctorate in 1900 and later joined the Reichsjustizamt.
From 1911, he was also the first Secretary General of the Kaiser Wilhelm Society for the Advancement of Science.
In 1919, he moved to the Foreign Office, where he was promoted to State Secretary in 1921. Ernst von Simson was involved in the signing of the Treaty of Versailles in 1919, the London Conference in 1921 and the Genoa Conference in 1922 - including the Treaty of Rapallo.
He left the civil service in 1922 and worked for Agfa, IG Farbenindustrie and national and international trade associations. In 1937, he was forced to resign from his offices and mandates.
In 1939, he and his wife emigrated to England/Oxford via Switzerland, where he died two and a half years later.